Isotopic Ratios in a Peculiar Outbursting Comet

Isotopic ratios in comets provide keys for the understanding of the origin of cometary material, and the physical and chemical conditions in the early Solar Nebula. A newly discovered peculiar comet, C/2015 ER61, underwent an outburst with a total brightness increase of 2 magnitudes on the night of April 4th, 2017. The sharp increase in brightness offers a rare opportunity to measure the isotopic ratios of the light elements of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES on Apr. 13 and Apr. 17 respectively. At the time of our observations, the comet was fading gradually since the outburst. We measured the 12C/13C and 14N/15N isotopic ratios from the CN Violet (0,0) band. In addition, we determined the 14N/15N ratio in NH2 for C/2015 ER61 from four pairs of NH2 isotopologue lines. Some 18OH lines were detected but the S/N of these lines is too low to derive a reliable 18O/16O estimate. We will present our UVES spectra of C/2015 ER61, obtained shortly after the outburst. We will also present the comparison of the Isotopic ratios of C/2015 ER61 with those of other comets.